The invention relates to a rolling-body screw drive having a threaded spindle and a threaded nut enclosing the threaded spindle, a helically running threaded channel provided between an outer circumferential surface of the threaded spindle and an inner circumferential surface of the threaded nut, the threaded channel forming, together with a return channel which connects the two end regions of the threaded channel, an endless circulatory channel in which an endless series of rolling bodies is accommodated, each of the two end regions of the threaded channel being assigned a deflecting element, which is retained in a recess or cutout in the threaded nut and has a deflecting channel, for transferring the rolling bodies between the threaded channel and the return channel and between the return channel and the threaded channel, and in which at least one of the cutouts for accommodating the deflecting elements is introduced into the threaded nut from the outer circumferential surface thereof and is bounded by the threaded nut in both directions running centrally parallel to the longitudinal axis of the threaded spindle.
Such a rolling-body screw drive is known, for example, from U.S. Pat. No. 2,166,106. The disadvantage with the rolling-body screw drive disclosed in this document is, in particular, its high-outlay production. Thus, first of all, it is necessary to produce the through-passage for the threaded spindle, and that part of the threaded channel belonging to the threaded nut has to be formed on the inner circumferential surface of the threaded nut. This machining of the threaded nut takes place essentially in the axial direction of the threaded nut. Then, in a sequence of operating steps carried out essentially in the radial direction, the mounts (cutouts) for the deflecting elements are provided by essentially radially running bores being introduced into the outer circumferential surface of the threaded nut. Furthermore, the deflecting elements of the known rolling-body screw drive are secured on the threaded nut by grub screws. For this purpose, once the deflecting elements have been inserted into the accommodating recesses or bores, it is necessary to introduce a further bore into the threaded nut, this further bore passing through both the boundary surface of the mount and the deflecting element inserted therein. Finally, an internal thread also has to be cut into this further bore.
The object of the present invention is thus to simplify the production of rolling-body screw drives of the foregoing type.
This object is achieved according to the invention by a rolling-screw drive of the type mentioned in the introduction in which at least one deflecting element is secured on the threaded nut by fastening means, preferably fastening pins, that run essentially parallel to the longitudinal axis of the threaded spindle. With the fastening means thus oriented parallel to the longitudinal axis of the threaded spindle, all of the production steps which have to be carried out on the threaded nut may be carried out in a single chucking fixture for the threaded nut, namely a chucking fixture which allows axial machining of the threaded nut. This simplifies the production of the threaded nut, which, inter alia, reduces the amount of time required for the production process and thus increases the number of threaded nuts produced per unit of time. Furthermore, there is an increase in the accuracy with which the threaded nut can be produced, since a change in the clamping situation with resetting of the workpiece during the production of a component constitutes one of the main causes of inaccuracy of the machined components. It is precisely the case with rolling-body screw drives, however, that the accuracy with which the individual elements, such as threaded spindle and threaded nut, are produced is decisive for the service life of the jointly formed subassembly.
As fastening means, use is preferably made of fastening pins since, for a mount, these merely require a blind hole or a bore, which can be introduced into the threaded nut in just a single operation. In principle, however, it is also possible to use other fastening means, e.g. screws, on the rolling-body screw drive according to the invention.
A straightforward production of the deflecting element is made possible if at least one of the deflecting elements is made up of at least two deflecting-element parts which together bound the deflecting channel. These deflecting-element parts may be designed without undercuts. The associated capacity for straightforward demolding of the deflecting-element parts makes it possible for the deflecting-element parts to be produced by injecting molding.
The deflecting element may, furthermore, comprise a main deflecting-element part, which serves, for example, for the fastening of the deflecting element on the threaded nut, and at least one secondary deflecting-element part. In this configuration of the deflecting element, it is possible to effect an advantageous separation of functions in the deflecting element. It is thus possible for the main deflecting-element part to be designed appropriately for the stressing conditions so that it can effectively absorb forces stemming from the fastening of the deflecting element on the threaded nut. It is likewise possible for the secondary deflecting-element part to be designed in a suitable manner particularly for the guidance of rolling bodies. For example, the divided design of the deflecting element allows the use, appropriate for the stressing conditions, of different materials for the deflecting-element parts.
The main deflecting-element part may advantageously be designed such that the fastening means pass through the main deflecting-element part. This further simplifies the production of the deflecting elements since through-passage openings which can be produced straightforwardly in just one operation, e.g. bores, are sufficient for the through-passage of a fastening component.
If, as a result of the fastening of the main deflecting-element part on the threaded nut, at least one secondary deflecting-element part is retained on the threaded nut by the main deflecting-element part, the secondary deflecting-element part may thus be relieved of all fastening functions and, accordingly, need not be provided with its own fastening means for fastening on the threaded nut. This reduces the number of operating steps required for producing the secondary deflecting-element part.
It is also possible for the deflecting element to be designed as a single part, with the deflecting channel running entirely in the interior of the deflecting element. It is also possible in this case to achieve the abovementioned advantages in the fastening of the deflecting element if there is provided a retaining element which secures the deflecting element in the mounting recess or cutout. For the reasons which have already been mentioned, it is advantageous here if the fastening means pass through the retaining element.
Particularly straightforward production of a rolling-body screw drive of the generic type is possible when the recess or cutout for accommodating the deflecting elements on the threaded nut comprises two surfaces running essentially orthogonally to the longitudinal axis of the threaded spindle and two concave surfaces which are essentially parallel to the longitudinal axis of the threaded spindle. An opening is provided between the essentially orthogonally running surfaces and between the two concave surfaces, and the helically running threaded channel is accessible through such opening. Such a cutout may be produced, for example, in a straightforward manner by milling, for example using a side-milling cutter, with the machine spindle which drives the milling cutter, in turn, running essential parallel to the longitudinal axis of the threaded spindle of the rolling-body screw drive. Although the cutouts for accommodating the deflecting elements are usually machined from both end sides, it is nevertheless possible, for example, to use a clamping device, which can be rotated through 180xc2x0, in a chucking fixture to produce them with the bores which are to be introduced into the threaded nut, without the workpiece having to be reset in the clamping device in the process. As a feature of the invention, it is thus possible not just for the deflecting elements to be fastened on the threaded nut in the axial direction, but, irrespective of this, also for the mounts for the deflecting elements to be introduced into the threaded nut in the axial direction
It should be also be added that, in order to produce the mounts for the deflecting elements, it is also possible to use a grinding process in addition, or as an alternative, to milling.
Depending on the tool which is used for machining the threaded nut of the rolling-body screw drive, collisions with tool and/or machine parts may occur during the production of the threaded nut. For example, the shank of the side-milling cutter may collide with the outer circumferential surface of the threaded nut, with the result that the side-milling cutter cannot penetrate into the threaded nut sufficiently deeply to produce a functional mount therein. Such collisions, in which both the tool used and the workpiece may be destroyed or at least damaged, can be prevented, for example, in that recesses for tool and/or machine parts may be provided on the threaded nut.
During the operation of the rolling-body screw drive, the threaded nut may be connected to a moveable component, for example a carriage or a ram, in a straightforward manner by means, for example, of a threaded extension at at least one of its longitudinal ends.
As has already been mentioned above, the deflecting-element parts may be produced, for example injection molded, from plastic. This allows straightforward and cost-effective production of the deflecting-element parts with the same high level of production accuracy.
Furthermore, the rolling bodies used in the rolling-body screw drive may be balls. Balls are preferably used in rolling-body screw drives since, in contrast to other rolling bodies, they do not have a preferred rolling direction which would have to be taken into account in the design of the rolling-body channel.